1. Field of the Invention
This invention relates to a novel cellulase, a CMCase isolated from the cellulase, and a microorganism capable of producing the cellulase.
2. Discussion of the Background
The term cellulases refers to a complicated enzymatic system. This enzymatic system is a catalyst for the enzymatic reaction by which cellulose and similar polysaccharides are decomposed into glucose, cellobiose or celloligosaccharides.
The term cellulases is considered to be a general name for enzymes which are called, depending upon their mechanism of activity, C.sub.1 enzyme, Cx enzyme and beta-glucosidase, or exo-beta-glucanase, endo-beta-glucanase, cellobiase and the like.
Cellulases have been studied mainly for the purpose of effectively utilizing biomass resources. For instance, the main source of cellulase supply has been fungi belonging to the genera Trichoderma, Aspergillus, Acremonium, and Humicola. However, cellulases deriving their origin from microorganisms including fungi involve a diversity of enzymes having differing working specificities and physiocochemical properties. The different enzymes which make up this enzymatic system have not yet been completely identified or studied.
Of these cellulases, those which have a high action on carboxymethyl cellulose (CMC) or Cx enzymatic action are generally called CMCases. In recent years, novel industrial utility for cellulases, including the CMCases, have been developed, particularly, as an additive for use in detergent compositions for clothing.
However, so far as cellulases produced by microorganism in nature and, particularly, the abovementioned cellulases originating from microorganism are concerned, they are, in most cases, so unstable that their activity is lost in an alkaline pH. These are so-called acidic and neutral cellulases (whose optimum working pH is in the range of 4 to 6). So-called alkaline cellulases which meet the requirement for detergent compositions for clothing, i.e. those which have a maximum activity and are resistant in an alkaline range, are very small in number.
For instance, with regard to alkaline cellulases which are usable in detergent compositions for clothing, there are only several known methods for producing alkaline cellulases originating from alkalophilic microorganisms. These methods include a method in which microorganisms belonging to the genus Bacillus are cultivated and cellulase A is collected from the medium (Japanese Patent Publication No. 50-28515). They also include a method in which alkalophilic bacteria belonging to the genus Cellulomonas are cultivated to produce alkaline cellulase 301-A (Japanese Patent Application Laid-open No. 58-224686), a method for producing CMCase by cultivation of alkalophilic Bacillus No. 1139 (Horikoshi et al, J. Gen. Microbiol., Vol. 131, page 3339 (1985)), and a method of producing an alkaline cellulase using a strain belonging to the genus Streptomyces (Japanese Patent Application Laid-open No. 61-19483).
There is thus a strong demand and need for cellulases having an optimum working alkaline pH and possessing enzymatic activity making them suitable for use in detergents for clothing in an alkaline range.